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mongodb - 多组聚合

问题描述

在我的数据库中有两种类型的会话-“工作室”、“教室”。我想要工作室课程的数量和课堂课程的数量以及课堂课程中的科目数量和工作室课程中的科目数量。

例如数据：

    [
  {
    "key": 1,
    "type": "studio",
    "sub": "english"
  },
  {
    "key": 2,
    "type": "studio",
    "sub": "history"
  },
  {
    "key": 3,
    "type": "classroom",
    "sub": "english"
  },
  {
    "key": 4,
    "type": "studio",
    "sub": "english"
  },
  {
    "key": 5,
    "type": "classroom",
    "sub": "english"
  },
  {
    "key": 5,
    "type": "classroom",
    "sub": "geography"
  }
]

这是我必须按会话类型分组的查询。

    db.collection.aggregate([
  {
    $group: {
      _id: "$type",
      groupedData: {
        $push: {
          key: "$key",
          "sub": "$sub",
          "type": "$type"
        }
      }
    }
  }
])

通过这个我得到

    [
  {
    "_id": "classroom",
    "groupedData": [
      {
        "key": 3,
        "sub": "english",
        "type": "classroom"
      },
      {
        "key": 5,
        "sub": "english",
        "type": "classroom"
      },
      {
        "key": 5,
        "sub": "geography",
        "type": "classroom"
      }
    ]
  },
  {
    "_id": "studio",
    "groupedData": [
      {
        "key": 1,
        "sub": "english",
        "type": "studio"
      },
      {
        "key": 2,
        "sub": "history",
        "type": "studio"
      },
      {
        "key": 4,
        "sub": "english",
        "type": "studio"
      }
    ]
  }
]

但我想要工作室和教室中的科目计数以及工作室和教室中的会话总数

例如。

{
  studio: { count: 3, englishInStudio: 2, historyInStudio: 1 },
  classroom: {count: 3, englishInClassroom: 2, geographyInClassroom: 1}
}

标签： mongodbmongoose

解决方案

您可以通过将文档指定为分组键来执行此操作

db.test.aggregate([
  { $group: {
    _id: { "type": "$type", "sub" : "$sub"},
     count: { $sum: 1}
   }
}]);

这将输出以下内容，这些内容会获取您所需的值，但格式不同：

{ "_id" : { "type" : "classroom", "sub" : "english" }, "count" : 2 }
{ "_id" : { "type" : "studio", "sub" : "history" }, "count" : 1 }
{ "_id" : { "type" : "classroom", "sub" : "geography" }, "count" : 1 }
{ "_id" : { "type" : "studio", "sub" : "english" }, "count" : 2 }

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